Say what you want, but an old commercial rule says that the customer is always right. And according to the customers, Kindle is a big hit. Amazon’s e-book reader that went on sale on Monday is already sold out and the customers seem to have fallen in love with the not-so-little gadget.

Amazon stayed mum on how many units have been sold so far, but on Kindle’s web page from the Amazon store there is a message saying that the stock will be refreshed on December 5, 2007. Of course, I can be mean and assume that Amazon hasn’t produced (ordered?) too many devices and the sold-out followed as a logical consequence. Also, as the shopping season started today, having a newly launched product that is already sold-out is not so good for a company.

But leaving aside those considerations, it seems like the Kindle device has generated a big buzz among Amazon’s book lovers, at least according to the product page. Of course some of them are complaining about PDF compatibility, the black and white screen, or about Kindle’s and the books’ prices. But it seems like eInk technology is quickly catching up amongst the users.

“First, anyone who thinks that a PDA or mobile phone with an LCD screen is "just as good" as a Kindle has never used a device with eInk technology. The Kindle's screen is very un-computer-like, and very much like reading paper. If you haven't seen one in person, you really can't comprehend how much easier on the eyes an eInk display is. It's effectively the difference between reading a laptop and reading a book... yes, it's that good” wrote an Amazon user in his Kindle review.

But others already have some suggestions for a new Kindle and having this amount of feedback on the product that is only four days old is good sign for Amazon.

Amongst the new required features, there are things like parental controls, security options, an alert system to notify the users when new books are available on Kindle store, an edition upgrade service, a service to trade in paper books for their electronic versions, a Kindle Store button and many more.

However until Amazon will come public with some sales figures it’s hard to tell how successful Kindle is.

In my opinion, if Amazon will be able to deliver a new version with a lower price soon, a better design and maybe if it’s possible, a color display, Kindle will do for books what iPod did for music, as Bezos hopes. Otherwise, Kindle will be just another gadget.